Direct synthesis of ({31 )-trans-{66 {11 tetrahydrocannabinol from olivetol and ({30 )-trans-{66 {11 -carene oxide

ABSTRACT

A one step stereospecific synthesis of Delta 9tetrahydrocannabinol by the condensation of olivetol with Delta 2-carene oxide is disclosed.

aeenfi [191 DHRECT SYNTHESIS OF (")-TRAN S-AQ- L ET m ATID P1ANS'-A CARENE OXIDE InVeniofsi Raj "Kiiiiiai mam, imam; G.

Ri c hqx d Handl-ick, Lexington, both of Mass.

Xs s ig hee: The United Staies of Aiiler i c a as represen t ed H the Secl etary of the Department of fleeliilfli dues tion and Welfare Filed: se e'izi, i971 Appl. No.: 182,841

ILLS. Cl ..260/345.3, 424/283 Int. Cl. ..C07d 7/24 Field of Search ..260/345.3

A one [111 J734fi$ 1 May 22, 1973 Primary Examiner-John M. Ford Attorney-Holman & Stem [5 7] STRACT step stereospecific synthesis of A tetrahydrocannabinol by the condensation of olivetol with A -carene oxide is disclosed.

7 Claims, No Drawings DIRECT SYNTHESIS OF ()-TRANS'A O9TETRAHYDROCANNABINOL FROM OLIVETOL AND (+)-TRANS-A -CARENE OXIDE This invention relates to the synthesis of tetrahydrocannabinol and more particularly to the synthesis of tetrahydrocannabinol by the condensation of olivetol with carene oxide.

Much has been written about marijuana and hashish and the physiological effects thereof. These materials are being used by ever-increasing numbers of people thereby leading to serious legal and sociological problems. Many of these problems are the result of ignorance of the effects and mechanisms of these materials. This ignorance, in turn, has resulted from a lack of proper scientific study.

10 thesizing tetrahydrocannabinol.

Several of these methods involve the preparation of A -tetrahydrocannabinol by the condensation of olivetol with either ()-verbenol or cis or trans-p-mentha- 2,8-dien-l-ol followed by the conversion of the same to 15 ()-trans-Atetrahydrocannabinol by the addition and elimination of hydrogen chloride. The reactions can be illustrated as follows:

A won HO- 05H ()verbenol olivetol HO- 0 H 4-trans-(2-olivetyl) pinene OII A -totrahydrocaunabinol IIO CH3 X l l I-IO- CHa- =CH2 (+)-p-menthadienol p-TSA I 1 3 4 Various other methods have been proposed, each reacted olivetol. Careful chromatography of this mixture quiring several steps and, therefore, being unduly cumon silica gel and elution with 60:40 hexane-benzene, bersome. followed by chromatography on Florisil and elution It is therefore a primary object of the present invenwith 2:98 ether-petroleum ether (bp 30-40), gives tion to provide a one-step method for the preparation 5 ()-A-THC (infrared nmr, glc, and tlc identical with of tetrahydrocannabinol. those of authentic material; [011D -245 (CHCl indi- It is another object of the present invention to procating an optical purity of ca. 95 percent). Since vide a one-step stereospecific synthesis of ()-trans-A"- A -THC has already been converted to ()-A-THC, as tetrahydrocannabinol. described above, this route constitutes yet another ste- Pursuant to the present invention, it has been found reospecific synthesis of (-)-trans-A-THC. that Oxide n be Condensed with It was then found that in the above condensation reolivetol in the presence Of an acid ca lys to form action, if the molar ratio of carene oxide is increased rahydrocannabinol. The reaction could be conducted (1,6 l/mol of olivetol), the major products formed without a catalyst, but a relatively high temperature, in are A .tran -Tl-[C (23 percent) d A -i THC the order of 140 C, is required. By using an acid catal5 gether with other products, but no A -THC is formed y the reaction can be fun at fairly low temperatures, (Scheme 1). Similar results are obtained by the addition the same generally being run in n i bath- Th acid of 1 percent boron trifluoride etherate in methylene catalyst could be boron trifluoride 01' p-toluenesulfonic chloride to an equimolar ratio of carene oxide and acid, although bOI'Oll trifluoride, as will be seen hereinolivetol in methylene chloride at room temperature,

below is P nerally he e ft qgigagfglQws: ?P The mixture of products thus obtained is chromato- Both of the starting materials are available commergraphed on Florisil and eluted with 2:98 ethercially, the carene oxide having been supplied by Glidpetroleum ether (-40). A fraction, [a]D 59 den and Co. Carene oxide can be prepared by the (Cl-iCl Contains trans-A -THC and cis-A -THC method of Arbuzov and Vilchinskaya, Izv. Akad.Nauk (60:40 ratio), as shown by gas chromatographic and SSSR, Ser. Khim., 954 (1967); cf Chem. Abstr., 68, nmr analyses and by conversion to A -THC and iso- 22063 (1968). THCs on treatment with p-toluenesulfonic acid in re- More specifically, it has been found that by allowing fluxing benzene. This fraction is separated by prepara- (+)-trans-2-carene oxide to react with an equimolar tive vpc (column 3.8 percent SE 30 on Diatoport S; quantity of olivetol in the presence of p-toluenesulfonie gas, helium; oven temperature, 240 to give ()-A- acid (0.05 mol/mol of olivetol) in benzene, a complex THC with an optical purity of 80 percent by comparimixture of products is obtained. This mixture contains son with the 0RD curve of an authentic sample. This 23% A -THC, 7% A-THC, 13 percent citrylidenecantherefore provides the first one-step synthesis of optinabis 11% cannabis iso-THC, and 34 percent unrecally active A'-THC.

no in H l-7 p TSA A-truns-Tll0 A-eis-llIC CsIIu 05H" T' s n on i 4+ l on on 1 7l\()/ ("5]Iu A AMmns-THC 'iso-THC lso-TIlC It is interesting to note that no cannabidiol is formed in any of these reactions and the ratio of trans to cis products is ca. 1.2 with p-toluenesulfonic acid, whereas it is ca. 0.6 (i.e., increase of cis products) with the use of boron trifluoride etherate. We interpret these results as suggesting that transand cis-A -THCs are first formed (Scheme lI and are then converted into their transformation products 3 and 5 7, respectively. This is in complete agreement with the known acidcatalyzed transformation in cannabinoids. Furthermore, the results suggest that the reaction has a more concerted character when a nonprotonic acid catalyst like BF is used, whereas acid catalysts like p-TSA, which gives a more carbonium ion character to the allylic system in the intermediate 9, give the trans products, which are more thermodynamically and kinetically stable.

A solution of 24.5 g (0.16 mole) of Z-carene oxide in 60 ml of benzene was added during 30 min. to a stirred solution of 18.0 g (0.1 mole) of olivetol and 0.3 g (0.00158 mole) of p-toluene-sulfonic acid monohydrate in 100 ml of benzene. The temperature was held at 1820 C by cooling the flask and contents in a water bath at -15 C. The solution was then heated to reflux under a Dean-Stark trap until the vapor temperature was 80 C and all water had been removed; about 45 min. was required. The cooled solution was washed to neutrality with water and dried over anhydrous sodium sulfate. Removal of solvent at reduced pressure left 38 g of a red-orange, cloudy resin. Analysis by gas chromatography showed this product contained about 10 percent each of unreacted olivetol, ciS-A -tetrahydrocannabinol, trans-A- tetrahydrocannabinol, A-"-tetrahydrocannabinol and isotetrahydrocannabinol. There was no peak corresponding to A -tetrahydrocannabinol.

This composition was confirmed upon examination of fractions obtained from a liquid-solid column chromatographic separation of 5 g of this red-orange resin or silica gel, eluted with 70:30 hexanezbenzene (loading ratio :1). The identifications were made by comparison of retention times in gas chromatography with retention times of authentic samples of the individual components. Additional confirmation of the cisand trans-M-tetrahydrocannabinols was obtained when one fraction (0.13 g), consisting of equal amounts of these two components, was heated in benzene solution with catalytic amounts of p-toluenesulfonic acid. Products of this treatment were shown, by gas chromatography, to consist of A -tetrahydrocannabinol and isotetrahydrocannabinols, which are the typical products formed from trans-M- and cis-A -tetrahydrocannabinol, respectively, when heated in an acid environment.

EXAMPLE 2 With stirring and cooling in an ice bath, 0.2 ml of 45 percent boron trifluoride etherate solution in 5 ml of 5 methylene chloride was added dropwise to a solution of 1.8 g of olivetol and 1.8 g of A -carene oxide in 15 ml of methylene chloride. The now brownish-red mixture was allowed to warm to room temperature. After 1 hour approximately'SO ml of ether was added and the 10 reaction was quenched by adding it to 10 percent so dium bicarbonate solution. The organic layer was separated, washed with sodium bicarbonate solution, and then with water to neutrality. It was dried and evaporated to leave a dark gum. This gum was chromato- 15 graphed on Florisil and eluted with 2:98 ether/petroleum ether (40). A fraction was isolated containing A -cis and A -trans-THCS (40:60 ratio) as shown by gas chromatographic and nmr analyses. The compounds were identified by glc on the basis of relative retention times of authentic samples and by addition of authentic samples to the reaction mixture with subsequent glc. The nmr showed a clear separation of signals at 8 (CDCI 1.08 (s, one of the geminal methyls) and 3.18 (br, d, C-3proton), which correspond to A -tranS-THC, and similarly 1.26 (s) and 3.56 (br) corresponding to A9C1S-THC. This fraction was further separated by preparative vpc (column, 3.8% SE 30 on Diatoport S; carrier gas, helium; oven temperature, 240) to give (-)-A-trans-THC with an optical purity of 80 percent by comparison with the optical rotatory dispersion curve of an authentic sample. Both 0RD curves were found to be parallel in the 280-600 mg region; [a]D -l 31 i 2 (cyclohexane); an authentic sample of ()-4 had [011D 148 i 2.

The invention now having been described by reference to certain preferred embodiments thereof, it is obvious the objects set forth at the outset of the specification have been met. The invention may be otherwise variously embodied and practiced, within the scope of the following claims.

What is claimed is:

1. A method for the stereospecific synthesis of A tetrahydrocannabinol comprising condensing olivetol with A -carene oxide.

2. A method as defined in claim 1, wherein said condensation is performed in the presence of an acid catalyst.

3. A method as defined in claim 1, wherein said catalyst is selected from the group consisting of boron trifluoride and p-toluenesulfonic acid.

4. A method as defined in claim 3, wherein said A- carene oxide and said olivetol are present in a molar ratio of 1.611 and said catalyst is p-toluenesulfonic acid.

5. A method as defined in claim 3, wherein said N- 3 ,734,930 7 8 carene oxide and said oliire iol are present in equimolar tetrahydrocannabinol. amounts. 7. A method as defined in claim 6, wherein said trans- 6. A method as defined in claim 1, further comprising and cis-A-tetrahydrocannabinol are separated by separating said A -tetrahydrocannabinol into trans-M vapor phase chromatography. tetrahydrocannabinol and cis-A- 

2. A method as defined in claim 1, wherein said condensation is performed in the presence of an acid catalyst.
 3. A method as defined in claim 1, wherein said catalyst is selected from the group consisting of boron trifluoride and p-toluenesulfonic acid.
 4. A method as defined in claim 3, wherein said Delta 2-carene oxide and said olivetol are present in a molar ratio of 1.6:1 and said catalyst is p-toluenesulfonic acid.
 5. A method as defined in claim 3, wherein said Delta 2-cArene oxide and said olivetol are present in equimolar amounts.
 6. A method as defined in claim 1, further comprising separating said Delta 9-tetrahydrocannabinol into trans- Delta 9-tetrahydrocannabinol and cis- Delta 9-tetrahydrocannabinol.
 7. A method as defined in claim 6, wherein said trans- and cis-Delta 9-tetrahydrocannabinol are separated by vapor phase chromatography. 